1. Field of the Invention
The invention relates to an engine with a variable valve timing mechanism, and particularly, to an engine with a variable valve timing mechanism having a chain case that covers a timing chain.
2. Description of the Related Art
In an engine that is mounted on a vehicle, a chain cover that covers a timing chain is attached to an engine body having a cylinder block and a cylinder head. Also, an engine has been known which has a variable valve timing mechanism (VVT) changing valve timing. The variable valve timing mechanism attaches a hydraulic actuator to an end portion of a cam shaft that is pivotally supported by a cylinder head, attaches a hydraulic control valve to a chain case that covers a timing chain and operates the actuator in accordance with a supply state of an operating oil from the hydraulic control valve, thereby changing the valve timing.
Patent Document 1: JP-A-2008-174116
Patent Document 2: JP-A-2008-215323
In a chain case structure for an engine according to Patent Document 1, a chain case is provided with a hydraulic control valve attachment part to which a hydraulic control valve is attached and a mount attachment part that bulges in a crank axis line direction and a fastener part is arranged between the hydraulic control valve and the mount attachment part. An engine with a variable valve timing mechanism according to Patent Document 2 has a structure where a chain case is provided with a mount attachment part that bulges in a crank axis line direction, an intake-side hydraulic control valve attachment part and an exhaust-side hydraulic control valve attachment part and the intake-side hydraulic control valve attachment part and exhaust-side hydraulic control valve attachment part are connected to a side of the mount attachment part. Also, a fastener part that fastens the chain case to en engine body (cylinder head) is provided above the mount attachment part or intake-side hydraulic control valve attachment part and below an actuator cover part.
According to the structure of Patent Document 1, the hydraulic control valve attachment part is provided above the mount attachment part and the fastener part is provided below the hydraulic control valve attachment part. Therefore, when a bolt is inserted into the fastener part and is strongly (excessively) tightened, a periphery of the hydraulic control valve attachment part is deformed due to an axial force (or fastening force) of the bolt. Hence, distortion may occur between the hydraulic control valve attachment part and the hydraulic control valve, so that the operating oil may be leaked to an outside from a port of the hydraulic control valve. As a result, it is not possible to secure a sufficient oil pressure (operating oil pressure) when changing a phase of the variable valve timing mechanism, so that the speed (responsiveness) of changing a phase of the variable valve timing mechanism may be lowered. Also, according to the above structure, since the mount attachment part is formed below the hydraulic control valve attachment part and fastener part, the mount attachment part is positioned at a center of the chain case in a height direction. Therefore, when supporting the engine in a pendulum mount (suspension) manner, the mount attachment part approaches an elastic principal axis in a roll direction of the engine. Hence, it is difficult to suppress large torque (or high torque), which occurs upon acceleration of a vehicle, so that it is not possible to reduce vibrations of the engine.
According to the structure of Patent Document 2, the fastener part is arranged in a flat area becoming a valley between an actuator cover part and the mount attachment part (or intake-side hydraulic control valve attachment part). Therefore, when the bolt is inserted into the fastener part and is strongly (excessively) tightened, the flat area becoming a valley between the actuator cover part and the mount attachment part (or intake-side hydraulic control valve attachment part) is weakened, so that a periphery of the fastener part is deformed or distorted due to the axial force of the bolt. Furthermore, the distortion may occur around the hydraulic control valve attachment part. Also, an engine-side mount bracket is attached to an upper side of the intake-side hydraulic control valve attachment part. Therefore, when a vehicle travels or the engine drives, the load or vibration of the engine-side mount bracket is directly transferred to the intake-side hydraulic control valve attachment part, so that the periphery of the intake-side hydraulic control valve attachment part is deformed due to the vibration and the operating oil may be thus leaked from the port of the hydraulic control valve to the outside. As a result, it is not possible to secure a sufficient oil pressure (operating oil pressure) when changing a phase of the variable valve timing mechanism, so that the speed (responsiveness) of changing a phase of the variable valve timing mechanism may be lowered. Also, according to the above structure, since only leading end portions of the intake-side hydraulic control valve attachment part and exhaust-side hydraulic control valve attachment part are connected to the mount attachment part, a recess part is formed at an inner side of the mount attachment part. Therefore, the rigidity of the mount attachment part is not sufficient and the mount attachment part is apt to vibrate due to the vibrations of the engine, so that it is not possible to obtain an effect of sufficiently lowering the vibrations of the engine.